On 26 Jul, 2006, at 07:34, John Anderson wrote:
I'm also in favor of getting rid of the redirectTo's and using
explicit attributes in their place.
Same here ... I think everyone's on board with this one :).
Bryan Stearns wrote:
There are a couple of things happening that are calling our
attribute-redirection strategy into question...
- Bug 6387 (sorted index doesn't maintain sort) where we're trying
to index a redirectTo attribute. I'm not sure what exactly is
happening, but I can imagine: existing attribute redirection
doesn't let the repository know when a redirect-source attribute
has changed, so that it can update a redirect-target index.
- The dashboard spec calls for more-complex multi-attribute
sorting on some columns; some of the sorts call for collection
indexes that will need to consider attributes on items other than
the one in the collection: eg, when sorting the date column, an
item needs to produce "the next interesting datetime", which could
be the startTime if it's an event, or the datetime of the next
tickler that's going to fire (and while the spec only calls for
one tickler per item for now, there'll be multiple ticklers in the
future).
I'm a little confused on "the next interesting datetime", but could
it be solved by having adding a new attribute
"interestingDateTime" (which the sort uses), and is possibly
updated whenever an event's startTime is modified or it's tickler
time is updated? This is what I proposed in bug#6387 and seems like
what Jeffrey is proposing below.
Sure. But how exactly would this work: i.e. onValueChanged(),
monitoring the changed values, or some other way? I'm a little wary
of onValueChanged() becoming overly complex. In general, we want to
index these attributes, so what I'd like to see is an API similar to
what's now pim.Calculated:
class MyContentItem(ContentItem):
def getInterestingDatetime(self):
# ... perform possibly complex calculation
return resultOfPossiblyComplexCalculation
# optional: setInterestingDatetime
interestingDatetime = schema.IndexedProperty(
schema.DateTime,
basedOn = ('startTime',
'ticklers'), # basedOn == attributes in Indexed.addIndex()
indexType = 'attribute', # could
be 'string',
fset = getInterestingDatetime)
This would create an attribute which is a property on the class, and
also create the appropriate index (named the same as the attribute).
Maybe it somehow caches the value so that getInterestingDatetime
doesn't get called every time the attribute is accessed (though it's
not clear that's necessary).
(FWIW, it's the index that ends up creating a monitor here to update
when changes are made to the "source" attribute).
--Grant
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